Book/Report

FZJ-2018-06306

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png MeV- Ionen induzierte chemische Reaktionen in festem Methan, Ethen und Ethin: theoretische und experimentelle Studien zur Wechselwirkung kosmischer Strahlung mit extraterrestrischen Eiskörpern

Kaiser, R.-I. (Corresponding author)FZJ*

1993
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag Jülich

Please use a persistent id in citations: http://hdl.handle.net/2128/19933

Report No.: Juel-2856

Abstract: The interaction of the low energetic particle component of cosmic radiation (1-10 MeV) with extraterrestrial icy bodies at 10 K was simulated in the laboratory in order to study the mechanisms of complexation of simple, primordial organic molecules. Model substances : methane, ethene and ethine were condensed in 3 $\mu$m layers on a silver single crystal plate at 10 K and were irradiated with 7.3 MeV protons and 9 MeV $\alpha$-particles from the Jülich compact cyclotron CV 28. The differentiation between thermal and suprathermal components of the reaction mechanisms was achieved by varying the following parameters: linear energy transfer LET (4-50 keV $\mu m^{-1}$), H:C ratio of target substances (4 to 1), temperature (10-50-293 K), dose (up to 150 eV per target molecule), and isotopic substitution (H, D, 12C, 13C). Theoretical studies on the collision cascades induced by the MeV particles were carried out with the computer simulation programs MARLOWE and TRIM. The UHV-irradiation apparatus (CRS, Cosmic Ray Simulator) allows for a gas condensation free of any contamination and a temperature control of the condensate within ± 0.5 K. Detailed information on the mechanisms of chemical reactions at the critical temperature of 10 K in space and particular in the interstellar medium or the early solar system, could be obtained. Suprathermal C, CH, and CH$_{2}$ species are formed by knock-on processes or Coulomb interactions and react in insertion and abstraction reactions to more complex compounds such as the methyl carbene radical CH-CH$_{3}$ which ist the source of C$_{2}$H$_{2}$, C$_{2}$H$_{4}$, C$_{2}$H$_{6}$, C$_{3}$H$_{8}$, etc. An important feature of this work ist the role of radiolytically produced H-radicals whose diffusion in CH$_{4}$ starts at the critical temperature range of 10-15 K. Their recombination with organic radicals at lowest temperatures hinders the build-up of more complex structures. When their concentration exceeds 6±3 %, i. e. at He$^{2+}$ doses > 120 eV per CH$_{4}$ molecule, they recombine spontaneously to H$_{2}$, thus, exploding the target. Linear energy transfer by nuclear collisions > 13±2 keV $\mu m^{-1}$ generates carbon atoms with energies up to 10 keV, which themselves generate 40-70 suprathermal secondary carbon atoms. On the average 10-20 of those are concentrated in defined volumes from 6x10$^{3}$ to 5x10$^{4}$ $\mathring{A}^{3}$. The interaction of suprathermal atoms and their products with the radicals of the general radiation damage in a collisionally excited part of the lattice leads to the formation of complex compounds such as polycyclic aromatic hydrocarbons in a concerted process, the so called multi center reaction. The overlap of individual reaction zones in a multibody interaction is of importance for the formation of heterocyclic compounds and other CHON species in mixed icemineral systems upon cosmic or solar radiation such as expected for comets.

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Contributing Institute(s):

1. Publikationen vor 2000 (PRE-2000)

Research Program(s):

1. 899 - ohne Topic (POF3-899) (POF3-899)

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